Picked up a used Sport II last week. Looks and manually cycled fine. Took it to the country today for a test run. Loaded up the mag with a box of TullAmmo .223 that I was given. Fired five rds. then, no trigger pull. Ejected the round and fired 6 more times and the same thing happened. did this several more times. It's picking up a round every time, but there is no trigger pull. I can return the rifle but would like to hear if there is a problem I can solve.

No#1 is to check that your bolt is in full battery first, if not disassemble and clean the bolt control group and breach , lube and reassemble test fire.

If the bolt is in battery place on safe and hinge your gun open to inspect the trigger group making sure the hammer hasnt slipped off the trigger sear , the AR15 hammer will engage the firing pin head if it slips its sear and lock the trigger group.

If the trigger is not resetting, could be a bad or missing disconnector spring, hammer or trigger spring installed incorrectly. Or could be just bad ammo.

Have you field stripped it and cleaned and lubed it thoroughly, including the bolt carrier group?. Do that, and try some brass cased ammo.

Google some AR 15 trigger replacement videos and see if all the trigger group parts (mainly the springs) are present and installed correctly.

I have never used Tul ammo but if that is steel case stuff like Bozz10mm said switch to brass case ammo ,
The laquer coating on that steel case stuff can gum up the chamber causing issues on an AR15.

Thanks for the quick reply. I will follow your directions tomorrow. I have NOT disassembled the bolt yet. I also picked up some Winchester 5.56 to try.

Thanks for all of the info. I am an AR15 newby. Have AK's and a PTR 91 that I am familiar with. Would like to keep this M&P if I can solve this issue. I will apply all of the suggestions ya'll have provided.

Ther AR15 is a very different design than the PTR91 (HKG3) and AK47 but there are a ton of good AR15 tutorials on Youtube,
if the problem persists after a good cleaning and switch to brass case ammo you can contact S&W to see if its covered under the lifetime service warranty.

PS with a good bore light also check that the chamber isnt gummed up with melted laquer from the steel case ammo as that would prevent your bolt from going into battery as well.

Probably just a dirty chamber. I hope that fixes it.

Using more lube might help as well. I had one AR that was tight and needed plenty of LSA to keep it functional until it had quite a few rounds through it.

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Hue 68 noli me tangere

If the bolt is picking up and fully seating an unfired round after firing , then the problem is not a failure to charge -- it's a failure to reset the trigger. Assuming the trigger is stock, try examining it for completeness then thoroughly cleaning the trigger group first.

Is this a brand-new rifle? If not, there's the possibility that a previous owner either modified the trigger too much or installed an adjustable grip bolt that is misadjusted. These things have a small Allen screw set in to them that is adjusted to take out most of the first, creepy take-up stage of the standard trigger, and if they are adjusted too fine, or if the adjustment screw is not Loc-tited after adjustment, they can prevent reset of the trigger in just the hit-and-miss fashion you describe.

The "melted lacquer" scenario is a thing of the distant past that will not occur if your ammo is of new manufacture.

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Pisgah

I am going to bet the trigger has been bubbha'd one way or another. The OP states it is a used gun so I would bet that the previous owner either modified the trigger or that they improperly reinstalled it after cleaning. Often newbies put springs in incorrectly.

I also agree 100% that the laquered ammo issue is a thing of the past and that it only happened when you were firing a high round count at a quick pace. You had to get the barrel pretty hot for it to be an issue back in the day.

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Use should dictate gear!